1. Field of the Invention
The invention relates to suspended ceilings having a grid of metal beams that support panels in grid openings, that are adapted for use in seismic prone areas. The ceiling of the invention is designed to remain intact during a seismic event.
2. Prior Art
Generally, in suspended ceilings, a grid of interconnected metal beams is supported by hang wires embedded in an upper structural ceiling. The beams of the grid extend from wall to wall, and at the wall ends, the beams are supported from a wall molding. The grid supports panels and lights in the grid openings. Such a ceiling is shown in U.S. Pat. No. 4,827,681, incorporated herein by reference.
In some areas of a building, such as hospital corridors, that are often up to twelve feet between walls, hang wires are generally not used in the space between the suspended ceiling and the structural ceiling. The hang wires interfere with structures that necessarily occupy such space, such as water lines, heating and cooling air ducts, electrical conduits, sprinkler systems, communication lines, and conduits for diagnostic systems. When it is absolutely necessary to use hang wires in such space to straddle structures, they are sometimes arranged with trapeze-like installations that are time-consuming to construct, and tend to further clutter the space, which is already congested.
In earthquake prone areas, a conventional way of supporting suspended ceilings up to eight feet in length in a corridor, and sometimes up to twelve feet, with a minimum of hang wires, is to secure the main beams at one end of the grid to a supporting wall designated a fixed wall, vertically and horizontally, by means of a wall molding. At the other end of the main beams, each beam simply rests on the horizontal ledge of an angle molding secured to a wall designated a slip wall, as disclosed, for instance, in U.S. Pat. No. 7,293,393, incorporated herein by reference. The horizontal ledge may be extended up to a two inch width.
In some instances, a perimeter clip is used to secure the ends of the beams to the wall molding. Such a clip is shown in U.S. Pat. No. 5,046,294, incorporated herein by reference. Such a perimeter clip is fixed on the wall molding at each end of a line of beams, and an end of a beam at the end of a line is fixed in a clip.
A hang wire is attached to the beam and to the structural ceiling a short distance inward from the slip wall. In a seismic event, if the beam is shaken off the ledge of the wall molding on the slip wall, the hang wire provides continued support.